The present invention relates to air ventilation and an improved air ventilation system which includes dehumidification.
ANSI/ASHRAE Standard 62-1989 was established to address the need for increased ventilation of buildings due to poor indoor air quality. Increased levels of contaminants from humans, fuel burning appliances, building materials and furnishings have resulted from the current construction practices which produce tighter, low leakage buildings. For example, studies have identified volatile organic compounds (VOCs) such as formaldehyde, continued exposure to which can cause illness and which can buildup in poorly ventilated spaces. Recommended ventilation rates range from about 0.3 air changes per hour to over 1.0 air changes per hour. The actual level of recommended outdoor air intake depends on the use, size and occupancy of the building.
Indoor air quality is also affected by the presence of living organisms in the circulated air. Bacteria, mold and mildew, for example, thrive on the damp air in air conditioning ducts. For this reason, reduction of humidity levels is not only a comfort concern but also a health concern. Homeowners can reduce their exposure to harmful bacteria, mold and mildew by regulating the humidity level within their homes.
Homeowners also are becoming more aware of the importance of including air ventilation systems within their homes. Therefore, there exists a need for smaller, less complex, less expensive ventilation and dehumidification systems that are appropriate for residential use.
Many dehumidifiers currently in use rely on refrigerated cooling coils or compression elements to dehumidify. Such refrigerating coils increase the complexity and expense of the units as well as the input energy necessary to operate the system. Dehumidification can be achieved with less expense by using desiccant materials. Desiccant materials can either absorb or adsorb moisture and then expel that moisture without the need for cooling coils.
Ventilators that use desiccant materials to dehumidify often suffer from freezing during use in winter or cold weather. Such freezing occurs when the outside fresh air being supplied to the system freezes moisture and condensation on the desiccant wheel or block. When this happens, prior art devices typically shut off the supply of fresh air and re-circulate warm air through the system until the desiccant defrosts. Such a prior art process has the disadvantage of interrupting the ventilating function of the device while the desiccant defrosts.
Dehumidifiers using desiccants typically shape the desiccant as a wheel. By rotating the wheel, which intersects two separate air streams, the desiccant material continually adsorbs moisture from one air stream and expels the moisture to the second air stream. It is important to keep the two air streams separate; otherwise contaminants from the exhaust air will mix with the incoming fresh dehumidified air. Therefore, the device must be carefully constructed to minimize mixing pollutants from the exhaust air stream with the fresh air.
U.S. Pat. No. 5,179,998, assigned to Deschamps Laboratories, Inc. discloses a heat recovery ventilating dehumidifier which provides fresh, cool, low relative humidity air to a building or room during warm weather, and warm fresh air during cold weather. Fresh air is drawn into the heat recovery ventilating dehumidifier, cooled and dehumidified by heat exchange by exhausting stale air in a first heat exchanger, then further cooled and dehumidified by passage through a refrigerant coil.
U.S. Pat. No. 5,193,610 to Morissette et al. relates to an apparatus for defrostable ventilation systems using warm interior air as defrost air for defrosting the system during cool weather. In particular, the patent describes an apparatus whereby, during a defrost cycle, the interior defrost air may circulate through both of the fresh air and exhaust air paths for delivery back into the building, i.e., the warm interior air may be confined to circulate from the interior of the building into the ventilation apparatus and back to the interior of the building.
In accordance with the present invention there is provided a ventilation and dehumidification system for ventilating fresh air to a conditioned space. The system is comprised of a desiccant wheel for dehumidifying incoming air by exchanging moisture from an inflow current of air with an outflow current of air. The desiccant wheel is both regenerated and defrosted by a regenerative heater which is placed to heat the outflow current of air before the outflow current passes through the desiccant wheel. The system includes blowers in order to motivate the inflow and outflow currents of air. The system may also include heat recovery means such as a heat transfer wheel or a motionless heat transfer core. The blowers can be arranged so as to create an air pressure differential between the inflow chamber and the outflow chamber so that any leakage of air between the two chambers will occur from the inflow chamber to the outflow chamber.